In a small bowl, whisk together balsamic vinegar, olive oil, Dijon mustard, minced garlic, salt, and black pepper to create the marinade.

Place the flank steak in a shallow dish or resealable plastic bag and pour the marinade over it. Seal and refrigerate for at least 30 minutes, or up to 2 hours for more flavor.

Preheat the grill to medium-high heat. Remove the steak from the marinade and discard the marinade. Grill the steak for about 5-7 minutes on each side for medium-rare, or until desired doneness.

Once cooked, remove the steak from the grill and let it rest for 5 minutes before slicing it thinly against the grain.

While the steak is resting, grill the corn (if using fresh) for about 5-7 minutes until charred, or heat canned/frozen corn in a skillet until warmed through.

In a large bowl, combine the mixed greens, cherry tomatoes, corn, sliced red onion, and chopped basil (if using).

Top the salad with the sliced steak and sprinkle with crumbled Gorgonzola cheese.

Drizzle with additional balsamic vinegar or olive oil if desired, and serve immediately.